Our goals are to understand ribosome function and structure at the molecular level. We plan to use the recently developed method of DNA hybridization electron microscopy to map the locations of specific regions of rRNA, as well as immunoelectron microscopy to map the locations of ribosomal proteins and the spatial arrangement of functional sites on the ribosome. By relating these sites to our knowledge of ribosome structure, and to the ribosomes of diverse organisms, we hope to gain a detailed understanding of the mechanism of protein synthesis. Our objective will be to relate the three dimensional structure of the ribosome to its function during protein synthesis. The small subunit is responsible for recognizing the initiation site on mRNA with the participation of initiation factors and fmet- tRNA, for binding aminoacyl tRNAs, for associating with the large subunit, and for regulating the translational fidelity of messenger reading. The large subunit binds the acceptor stem of aminoacyl tRNAs entering the A site; catalyzes peptidyl transfer, and participates in elongation and translocation. By relating the three dimensional distributions of ribosomal proteins, factors, and regions of RNA's with known biochemical information, we will attempt to elucidate the structural aspects of the molecular events occurring during protein synthesis. Comparative studies of ribosome structure will also be pursued in order to relate structural features of prokaryotic, eukaryotic, and organellar ribosomes to their common functions in protein synthesis. Because these studies are so broad and relate to fundamental cellular mechanisms, we expect that they will be basic to all aspects of human health. Protein synthesis is a central part of the mechanism of all cells, and we hope our results can be broadly useful in diverse endeavors that range from treating diseased or abnormally growing human cells to controlling bacterial infections.